Scanning electron microscope

Abstract

A scanning microscope is provided for producing a scan image at high spatial resolution and in a low acceleration voltage area. An acceleration tube is located in an electron beam path of an objective lens for applying a post-acceleration voltage of the primary electron beam. The application of an overlapping voltage onto a sample allows a retarding electric field against the primary electron beam to be formed between the acceleration tube and the sample. The secondary electrons generated from the sample and the secondary signals such as reflected electrons are extracted into the acceleration tube through the effect of an electric field (retarding electric field) immediately before the sample. The signals are detected by secondary signal detectors located upwardly than the acceleration tube.

What is claimed is: 
     
       1. A scanning microscope for obtaining an image of a specimen from electrons reflected and/or generated from said specimen by irradiating said specimen with an electron beam discharged from an electron source, comprising: a sample holder disposed below said sample and supporting the lower surface of said specimen, said sample holder including a conductive member underlying all of said sample;   an electrode disposed above said specimen extending perpendicularly to the irradiating direction of said electron beam and having a periphery extending beyond a periphery of said specimen, said electrode having an aperture for passing said electron beam;   at least one electron detector disposed on the side of said electrode closer to said electron source; and   a negative voltage source applying substantially the same negative voltage to said sample holder conductive member and said electrode.   
     
     
       2. A scanning microscope as claimed in claim 1, wherein said electron beam is deflected to form a moving trace on said specimen and said electrode extends in the direction of said moving trace of said electron beam on said specimen. 
     
     
       3. A scanning microscope as claim in claim 2, wherein the periphery of said electrode is extended beyond the periphery of said specimen a sufficient amount to cover an area of movement of said specimen. 
     
     
       4. A scanning microscope as claim in claim 1, wherein the periphery of said electrode is extended beyond the periphery of said specimen a sufficient amount to cover an area of movement of said sample. 
     
     
       5. A scanning microscope as claimed in claim 1, wherein said electrode is formed to accommodate the shape of an objective lens located under said electron source. 
     
     
       6. A scanning microscope as claimed in claim 1, wherein said electrode is formed along the inner surface of a sample chamber enclosing said sample. 
     
     
       7. A scanning microscope as claimed in claim 1, said conductive surface located under said specimen is almost the same size or larger than the sample. 
     
     
       8. A scanning microscope for obtaining an image of a specimen from a electrons reflected and/or generated from said specimen by irradiating said specimen with an electron beam discharged from an electron source, comprising: a sample holder having a surface on which said specimen is disposed, and movable in a direction perpendicular to the irradiation direction of the electron beam, said sample holder including a conductive member underlying all of said specimen,   an electrode disposed along the path of said electron beam to the specimen when said specimen is moved by the sample holder, said electrode having a peripheral dimension larger than the periphery of an area over which said specimen can be moved, and having an aperture for passing said electron beam,   at least one electron detector disposed on the side of said electrode closer to said electron source, and   a negative voltage source applying the same negative voltage to said sample holder conductive surface and said electrode.   
     
     
       9. A scanning microscope for obtaining an image of a non-conductive specimen from electrons reflected and/or generated from said specimen by irradiating an electron beam discharged from an electron source, comprising: a specimen table having a surface for supporting said non-conductive specimen having a periphery extending beyond the periphery of said specimen, said table including a conductive member underlying all of said sample;   an electrode disposed between said specimen table and an objective lens for converging said electron beam, perpendicular with respect to an irradiating direction of said electron beam, said electrode having a periphery larger than said specimen periphery and having an aperture for passing said electron beam;   at least one electron detector disposed on the side of said electrode closer to said electron source; and   a voltage source applying a voltage to said specimen table and said electrode, wherein said specimen table and said electrode are so disposed as to make a space in which said specimen is disposed at a negative voltage and with almost no electric field.   
     
     
       10. A scanning microscope for obtaining an image of a specimen from electrons reflected and/or generated from said specimen by irradiating an electron beam discharged from an electron source, comprising: a specimen table having a surface for supporting said specimen having a periphery extending beyond the periphery of said specimen, said table movable in a direction perpendicular to an irradiation direction of said beam, said specimen table including a conductive member underlying all of said specimen;   an electrode disposed between said specimen table and an objective lens for converging said electron beam, perpendicular with respect to an irradiating direction of said electron beam, said electrode having a periphery larger than a periphery of an area over which said specimen can be moved and having an aperture for passing said electron beam;   at least one electron detector disposed on the side of said electrode closer to said electron source; and   a voltage source applying a voltage to said specimen table conductive member and said electrode, wherein said specimen table and said electrode are so disposed as to make a space in which said specimen is disposed at a negative voltage and with almost no electric field.   
     
     
       11. In a specimen observing method using an electron beam apparatus forming a specimen image based on electrons obtained from irradiating a portion of a non-conductive specimen with an electron beam, said method comprising the steps of: disposing said specimen between two electrodes having peripheries which extend beyond a periphery of said specimen, and disposed perpendicular with respect to an irradiating direction of said electron beam onto said specimen,   disposing at least one electron detector on the side of said electrode closer to said electron source, and   irradiating said specimen with said electron beam while making the region in which said specimen is disposed a negative potential region with substantially no electric field by applying a negative voltage to said two electrodes.   
     
     
       12. A scanning microscope for obtaining an image of a specimen from electrons reflected and/or generated from said specimen by irradiating said specimen with an electron beam discharged from an electron source, comprising: a sample holder disposed above said sample and supporting the lower surface of said specimen, said sample holder including a conductive member underlying all of said sample;   an objective lens for focusing said electron beam and having magnetic poles divided into an upper magnetic pole and a lower magnetic pole;   a negative voltage source applying substantially the same negative voltage to said sample holder conductive member and said lower magnetic pole;   wherein said lower magnetic pole extends perpendicularly to the irradiating direction of said electron beam and has a periphery extending beyond a periphery of said specimen.   
     
     
       13. A scanning microscope for obtaining an image of a wafer from a electrons reflected and/or generated from said wafer by irradiating said wafer with an electron beam discharged from an electron source, comprising: a sample holder disposed below said sample and supporting the lower surface of said wafer, said sample holder including a conductive member underlying all of said sample;   an electrode disposed above said wafer extending perpendicularly to the irradiating direction of said electron beam and having a periphery extending beyond a periphery of said wafer, said electrode having an aperture for passing said electron beam;   at least one electron detector disposed on the side of said electrode closer to said electron source; and   a negative voltage source applying substantially the same negative voltage to said sample holder conductive member and said electrode.